for me, it goes like this:
i can't stand the first gen. nearly all the original 151 just bore me to peices and i just can't have fun playing them anymore.
the second gen is alright. the graphics improved, you could choose your gender [crystal], and you could travel to kanto aswell as johto. but most of the second gen pokemon don't thrill me that much anymore either.
the third generation, i didn't much care for in the beginning. i mean, the graphics were great and the new pokemon were pretty cool, but i just never really found it thrilling to play and idk why. :\
the fourth generation is my favourite, and quite honestly i can't see how so many people on this board don't like it. it has amazing graphics, [for the most part] all of the pokemon look great, there are so many new options for the game, and so much more!